This application is based on applications No. 11-49818 filed in Japan on Feb. 26, 1999 and No. 11-91624 filed on Mar. 31, 1999, the contents of which are incorporated herein by reference.
This invention relates to a battery pack containing a rechargeable cell and a protection circuit.
A battery pack containing a protection circuit has been developed (Japanese Non-examined Patent Publication HEI 8-329913, 1996). As shown in FIG. 1, the battery pack disclosed in this patent application contains a prismatic battery 1016, which is a lithium ion rechargeable cell, and a protection circuit 103. The protection circuit 103 detects battery current and voltage and controls the system to avoid use of the battery under abnormal conditions. The protection circuit 103 prevents battery over-charge and over-discharge, or controls the system to avoid extremely large current flow through the battery. To control current flow through the battery, the protection circuit 103 utilizes a switching device such as a field effect transistor (FET) connected in series with the battery. The switching device is controlled by a control circuit. The control circuit detects battery voltage or current and controls the switching device on or off. When the control circuit turns the switching device off, current flow through the battery is cut-off.
The battery pack shown in FIG. 1 has a surface mounted protection circuit 103 on a printed circuit board 1017 disposed between the prismatic battery 1016 and a case 101. The printed circuit board 1017 has a large number of electronic parts attached to implement the switching device and the control circuit to turn that switching device on and off. Further, insulating paper 1018 is disposed on both sides of the printed circuit board 1017 to insulate the electronic parts attached to the printed circuit board 1017.
Since the switching device and control circuit are mounted on the surface of the printed circuit board of the battery pack shown in FIG. 1, the protection circuit can fail to function properly due to the electrolyte leaking from the battery. This is because the electrolyte can cause corrosion of metal regions attached to the printed circuit board surface, or cause short circuits between conducting regions due to migration or dendrite growth. Since the protection circuit protects the battery against use in abnormal circumstances, it is critical for the protection circuit to function properly in the abnormal situation when the electrolyte leaks from the battery. Therefore, it is important for the protection circuit to reliably protect the battery even when the electrolyte leaks from the battery.
In addition, moisture ingress can occur during battery use. Similar to electrolyte leakage, moisture ingress can adversely affect the protection circuit""s electronic parts, or corrode metal regions to interfere with proper functioning of the protection circuit. This drawback can be eliminated by making the battery pack case a completely hermetic structure. However, a completely hermetic structure cannot be made because of the requirement to expose terminals, such as the electrode terminals outside the battery pack case. Therefore, how to have a proper functioning protection circuit when moisture ingress occurs is extremely important.
Further, it is extremely difficult to make a battery pack, which has a switching device and protection circuit surface mounted on a printed circuit board, with a structure sufficiently resistant to vibration. This is because when the battery pack is vibrated, the electronic parts of the switching device and the protection circuit that are connected to the printed circuit board are also vibrated. Since electronic parts are attached to conducting layers on the surface of the printed circuit board, there is also the drawback that vibration can easily delaminate conducting layers. Consequently, it is possible for the electronic parts of the protection circuit that are surface mounted to a printed circuit board to become damaged or disconnected in a battery pack, which is assembled by a method that imparts vibration such as ultra-sonic welding of the case.
Still further, because prior art battery packs have large protection circuits, restrictions are placed on the location of parts within the case. For this reason, parts cannot always be located in ideal locations. For example, it may not be possible to place the protection circuit at its closest position to the connecting parts. Consequently, drawbacks may include a need for long protection circuit connecting leads.
The present invention was developed to eliminate these types of drawbacks observed in prior art battery packs. Thus, it is an important object of the present invention to provide a battery pack, which drastically reduces protection circuit malfunction generated by battery electrolyte leakage and moisture ingress, and which has a structure of superior resistance to vibration.
Another important object of the present invention is to provide a battery pack in which the protection circuit can be made extremely compact and can be freely located within a case with a water resistant, vibration resistant, and insulating structure.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The battery pack of the present invention has a case containing a rechargeable cell along with a protection circuit provided with a switching device, which is connected in series with the rechargeable cell and controls current flowing through the battery, and a control circuit, which detects battery voltage, or current, or both, and controls the switching device. The protection circuit, provided with a switching device and a control circuit, is molded with insulating material into a single package as a one-package unit. The one-package unit is disposed in a space provided in an insulating holder. The one-package unit, the insulating holder, and the battery are housed within the case.
A battery pack with this structure drastically reduces protection circuit malfunction caused by battery leakage or moisture ingress. This is because the protection circuit, provided with a switching device, which controls current through the battery, and a control circuit, which controls the switching device, is molded with insulating material into a single package, and housed along with the rechargeable cell in the battery pack case. Since the protection circuit is molded with insulating material into a single package, introduction of an electrolyte leaked from the battery, or moisture into the protection circuit, can be effectively prevented in a battery pack of this configuration. Consequently, this type of battery pack drastically reduces protection circuit malfunction or failure due to battery leakage or moisture ingress, and the battery pack can be used reliably over a long period. Further, since the protection circuit is molded with insulating material, this type of battery pack reliably fixes the switching device and control circuit in specific locations, and attains a structure with superior resistance to vibration.
In addition, since the protection circuit, provided with a switching device and control circuit, is molded with insulating material into a single package, the protection circuit can be made extremely compact in a battery pack of this configuration. Consequently, this type of battery pack has the characteristic that the protection circuit has a water resistant, vibration resistant, insulating structure, and can be easily positioned without restriction within the case.
The rechargeable cell is preferably a prismatic lithium ion battery. The case is, for example, an ultra-sonically welded plastic case. The protection circuit is, for example, molded in epoxy resin.
The one-package unit is covered with insulating material on both the top and bottom, and one end of the one-package unit lead material is embedded within the package. Lead material from the one-package unit is connected to the rechargeable cell and to the battery pack electrode terminals.
The insulating holder provides space in an opening on the side facing the rechargeable cell, and the one-package unit can be disposed in this space.
The one-package unit can be to fixed to a printed circuit board, and lead material can be attached to the printed circuit board. This one-package unit can be inserted into the insulating holder while attached to the printed circuit board.
The one-package unit can be rectangular with surface electrodes B+, Bxe2x88x92, and Vxe2x88x92 in corner regions of the bottom side. Surface electrodes B+ and Bxe2x88x92 for connection to the positive and negative sides of the rechargeable cell are preferably located at opposite ends of the one-package unit.
The battery pack can house, in its case, a thin outline battery as the rechargeable cell. Leads to connect the one-package unit with the rechargeable cell can be disposed along a side edge of the wide surface of the rechargeable cell. In the present patent application, a thin outline battery is taken to mean a battery having an external shape with thickness smaller than its width.
Finally, the battery pack can house, in its case, a thin outline battery as the rechargeable cell, and the one-package unit can be of rectangular shape. Lead material can be connected to the rectangular one-package unit projecting from its ends in the lengthwise direction. Lead material projecting from the ends of the one-package unit are connected to electrodes projecting from the rechargeable cell. The rectangular one-package unit is disposed parallel to the end of the long narrow rechargeable cell within the space provided by the insulating holder.